A vehicle is provided with a secondary battery that temporarily stores electric energy generated by an electric generator connected to an internal combustion engine via a belt or the like, for supplying required power to electric devices even when the internal combustion engine is not rotating and power cannot be generated by the electric generator, for example.
If such a secondary battery is over-charged or over-discharged, deterioration in the battery is accelerated. Therefore, in the case of using a secondary battery, it is necessary to perform charging or discharging so that the state of charge SOC of the secondary battery will not become an over-charged state or an over-discharged state.
As means for detecting the SOC of the secondary battery, there is known means of calculating the SOC based on secondary battery voltage detected by a voltage sensor.
However, in the above detection means, if the voltage sensor has failed, charging or discharging is performed based on an erroneous SOC, and therefore the SOC of the secondary battery may become an over-charged state or over-discharged state.
Therefore, such an SOC detection apparatus having a voltage sensor is provided with a device for detecting failure in the voltage sensor.
Patent Document 1 discloses a failure detection apparatus that calculates an electromotive force and an internal resistance of a secondary battery based on charge/discharge current of the battery detected by a current sensor and voltage of the battery detected by a voltage sensor, calculates estimated battery voltage of the secondary battery based on the electromotive force and the internal resistance, compares the estimated battery voltage with the battery voltage detected by the voltage sensor, and if a difference therebetween is equal to or greater than a predetermined value, determines that the voltage sensor has failed.